Methods of making polyvinylidene fluoride (PVDF) membranes and their use as filter media are known. See, for example, U.S. Pat. Nos. 4,203,847, 4,203,848 and 4,384,047. Various methods of rendering PVDF membranes hydrophilic are also known. For example, U.S. Pat. No. 4,943,373 discloses the use of a strongly alkaline solution of potassium permanganate for 3 to 10 minutes at temperatures up to 100.degree. C.